In the oil and gas industry apparatus is typically run in downhole on strings, such as drill strings, wire strings, coil tubing strings, or the like. Many downhole operations require the actuation of equipment in downhole locations at specific phases or positions of downhole operations.
Actuation of tools downhole is commonly achieved through various means. For example, downhole actuation may occur at a predetermined location such as a depth or relative to other downhole apparatus or features, such as when a tool being run-in reaches a previously-positioned tool or feature.
Other forms of downhole actuation involve remote actuation, such as from surface. Forms of remote actuation from surface include the use of flowable objects transported by fluid in a bore, pressure pulses or variations in properties of a fluid transported in a bore, hydraulic control by hydraulic lines, or signals sent by other means from surface. Examples of flowable objects transported by a fluid in a bore include drop balls, darts, plugs, RFID tags, or the like. Such flowable objects are inserted into the bore and transported to a downhole location by a flow of fluid (and typically gravity) in the bore when it is desired to use such flowable objects to actuate a downhole tool.
Downhole actuation is used to actuate various apparatus, such as valves. The valves may be for varying restriction sizes or for opening or closing ports, such as to redirect fluid to different flow paths or to actuate other apparatus.